1. Field of the Invention
The present invention relates to a method and apparatus for processing substrates while controlling the deflection (amount of warping or tilt angle) that occurs in the substrates during bonding of the individual substrates of, for example, optical disc substrates so as to attain a desired deflection.
Priority is claimed on Japanese Patent Application No. 2003-433599, filed Dec. 26, 2003, the content of which is incorporated herein by reference.
2. Description of Related Art
An optical disc for a DVD is known wherein two individual substrates having a recording layer, or one individual substrate having a recording layer and one individual substrate not having a recording layer, or an individual substrate having a recording layer and a sheet film, or one individual substrate and another individual substrate (here, these are also referred to as “individual substrates”) are bonded together by having interposed a photo-curable adhesive layer therebetween (for example, refer to Japanese Unexamined Patent Application, First Publication No. Hei 5-20714).
To read the data recorded on an optical disc or to record the data on an optical disc, the optical disc is irradiated externally by a laser while the optical disc is rotated, and the laser irradiates the recording layer by penetrating the transparent substrates of the optical disc. Because the recording density of the optical disc is extremely high, the laser must irradiate the recording layer with high precision. If the flatness of the optical disc is substandard, naturally the flatness of the recording layer will also become substandard. The laser will not be able to irradiate the recording layer in correct alignment with a predetermined position, and errors will occur when writing and reading the data. For this reason, when manufacturing the optical disc, generally there must not be warping or distortion and that a high degree of flatness can be maintained.
Various inventions have been proposed as methods for decreasing such warping during the manufacture of an optical disc. In one of these, a method is proposed in which the heat of the substrates, whose temperature has risen due to the irradiation of the curing light during the bonding of the individual substrates, is dissipated into the mounting table on which the substrates is mounted. After the ambient temperature and the temperature of the substrates have become substantially equal, the substrates are removed from the mounting table. In this method, this mounting table is cooled by using a cooling medium such as air or cooled water, and thereby the temperature of this cooling medium is controlled (for example, refer Japanese Unexamined Patent Application, First Publication No. Hei 10-199053).
Another method has been proposed wherein the mounting table on which the substrates are mounted is cooled so as to maintain a constant temperature (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2003-99985).
In another invention that decreases the warping during the manufacturing of an optical disc described above have been proposed. The invention includes a method has been proposed wherein the temperature of at least one of the surfaces of the substrates is controlled while the photo-curable adhesive layer interposed between the individual substrates of the optical disc is being cured, and thereby the temperature of both surfaces is controlled; a method has been proposed wherein the temperature of the substrates is controlled, and thereby the temperature distribution in both directions of the substrates is made uniform; and an apparatus has been proposed that provides a temperature control device that can adjust the surface temperature of a mounting table (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2000-76710).
However, due to increasing the flatness of the optical disc because of implementing the methods described above during manufacture of the optical disc, even if the optical disc possesses the required flatness immediately after its manufacture, during the subsequent storage, management, and distribution, the optical disc may warp in a predictable manner. For example, warping may occur due to label printing after bonding. In such a case, it is necessary to control the warping of the optical disc by taking into account the warping of such an optical disc during the final usage, and compensating warping must be intentionally applied to the optical disc so that almost no warping is present during the final usage.
In consideration of the problems described above, it is an object of the present invention to control the deflection (tilt angle) of the optical disc during manufacture so as to attain a target deflection.